1. Field of the Invention
The subject invention relates to a process for the production of low-cholesterol milk fat by solvent extraction. The invention also relates to low-cholesterol milk fat product produced by the process of the invention.
2. Description of Related Art
Milk fat-containing foods are popular with consumers. Consumers prize the distinctive organoleptic properties of milk fat. For example, butter, which is an emulsion of milk fat and water, is highly prized for its properties as a condiment. However, milk fat contains the sterol cholesterol. Recently, cholesterol has been identified as being potentially deleterious to human health when ingested in excessive quantities. Some consumers have therefore become hesitant about utilizing cholesterol-containing products.
Others have recognized the desirability of reducing the cholesterol content of animal fats, including milk fat. However, these methods have proven to be less than satisfactory because the organoleptic properties of the product typically differ significantly from the properties of the natural product. For example, mouth feel, melting point, or color may be significantly altered by the cholesterol removal technique.
A satisfactory cholesterol removal process preferably would maximize removal of cholesterol while minimizing alterations to the properties of the cholesterol-containing product to yield a low-cholesterol product indistinguishable from fresh, natural product. However, known cholesterol-removing processes typically make significant changes in products or organoleptic characteristics.
Fractionation of fats has been used to obtain separate component portions, typically so that the portions can be selectively recombined to yield a product having pre-selected characteristics. For example, the solvent-assisted fractionation disclosed in U.S. Pat. No. 4,005,228 is utilized to separate butter fat into fractions by melting point, i.e. melting point less than 0.degree. C., between 0.degree. and 20.degree. C., and above 20.degree. C. The high- and low-melting fractions are combined to yield a dairy spread.
Supercritical extraction has also been utilized to modify various foodstuffs, including butter, as described in U.S. Pat. No. 4,504,503. However, one of the drawbacks to this technique is that conditions which maintain the solvent in the supercritical region typically involve extremes of temperature and pressure. Therefore, the equipment required is expensive. For example, in this patent, the preferred temperature range is from 40.degree. to 250.degree. C., while the preferred pressure range is from 100 to 400 bar.
British patent specification No. 1,559,064, an improvement of GB No. 1,525,315, discloses the use of molecular distillation to reduce the cholesterol content of a medium containing fats. After degassing, anhydrous fat is subjected to molecular distillation at a pressure less than 0.005 Torr to remove the unsaponifiable fraction, which contains the sterols. Then, in accordance with the method of GB No. 1,525,315, an aqueous medium having a viscosity of from 2000 to 20,000 cp measured at a temperature between 20.degree. and 30.degree. C. is mixed into the treated fat at a temperature between 15.degree. and 45.degree. C.
Both U.S. Pat. No. 2,613,215 and EP No. 0 174 848 A2 teach that cholesterol can be removed from fats by contacting the fat with a solid absorbent or adsorbent material. Silica gel and activated carbon are utilized as examples of appropriate material.
The above-described methods for cholesterol removal are unsatisfactory. Previously, those wishing to remove cholesterol from milk fat typically started with butter. However, churning distributes the cholesterol within the fat, thus diluting it. In contrast, in an undisturbed milk fat globule, free cholesterol, which comprises about 90 percent of the cholesterol in butter fat, is located primarily in the milk fat globule membrane.
Milk fat is known to comprise a plurality of globules, each surrounded by a milk fat globule membrane. Dapper et al., "Use of Polar Aprotic Solvents to Release Membranes from Milk Lipid Globules," J. Dairy Sci. 70:760 (1987) disclose that aqueous solutions of selected polar aprotic solvents release milk fat globule membranes from milk fat globules. The properties of these chemically-released milk fat globule membranes were compared to the properties of milk fat globules released by churning and by successive freeze/thaw cycles. However, there was no suggestion about removal of cholesterol from the milk fat globule membranes.
Keenan et al., "Biochemical and Morphological Comparison of Plasma Membrane and Milk Fat Globule Membrane from Bovine Mammary Gland," J. Cell. Bio. 44:80 (1970) used solvent systems to obtain chromatographic separation of milk fat membrane lipids after separation of the membranes from the remainder of the milk fat. However, neither disclosure suggests selective extraction of cholesterol from substantially intact milk fat globule membranes.
Shishikura, "Modifications of Butter Oil by Extraction with Supercritical Carbon Dioxide", Agric. Biol. Chem. 50:1209 (1986), notes that supercritical fluid extraction using carbon dioxide is useful for fractionation of triglycerides in butter oil according to carbon number, but that this technique does not separate cholesterol from the triglycerides. Instead, butter oil was contacted with supercritical carbon dioxide and silicic acid. However, this supercritical technique not only lowered the cholesterol level, but also affected the triglyceride distribution. Thus, the technique is unsatisfactory, because the composition and spreadability are affected.